Session: 12-28-01: Functional Soft Composites - Design, Mechanics, and Manufacturing

Paper Number: 147281

147281 - Surface Embedded Metal Nanowire – Liquid Metal – Elastomer Hybrid Composites for Stretchable Electronics 

Both liquid metal (LM) and metallic filler-based conductive composites are promising stretchable conductors. LM alloys exhibit intrinsically high deformability, but present challenges for patterning on polymeric substrates due to high surface tension. On the other hand, conventional conductive composites comprising only one type of metallic fillers undergo considerable decrease in electrical conductivity under mechanical deformation. These single-filler composites also require high filler loading to reach percolation, which compromises stretchability of the elastomer-based composites. To countervail these issues, conductive composites with more than one type of conductive fillers have been developed, termed as hybrid-filler (or hybrid) composites. Hybrid composites with multiple fillers can synergistically improve the mechanical and electrical performances of composites. In particular, additional fillers such as LM can bridge the gaps between the primary fillers and can thus improve the electromechanical behavior of the composite, i.e., a more stable conductivity under strain. Among metal-based conductive fillers, metal nanowires with high aspect ratio such as Ag nanowires (AgNWs) have received considerable attention due to their high electrical conductivity and ability to form percolation network at relatively low threshold. Therefore, in this work, we present AgNW-LM-elastomer hybrid composite films, where AgNWs and LM are embedded below the surface of an elastomeric matrix, using two fabrication approaches, sequential and mixed. We investigate and understand the process-structure-property relationship of the AgNW-LM-elastomer hybrid composites fabricated using two approaches through morphological characterization, electrical conductivity, electromechanical stability, and mechanical robustness. Different weight ratios of AgNWs and LM provide tunable electrical conductivity. Moreover, different weight ratios of AgNWs and LM produce different surface roughness profiles, which dictate the formation of a uniform coalesced LM particle layer. The hybrid composites show more stable electromechanical performance than the composites with AgNWs alone. In particular, 1:2.4 (AgNW:LMP w/w) sequential hybrid composite shows electromechanical stability similar to that of the LM-elastomer composite, with a resistance increase of 2.04% at 90% strain. The sequential approach is found to form AgIn₂ intermetallic compounds which along with Ga-In bonds, impart large deformability to the sequential hybrid composite as well as mechanical robustness against scratching, cutting, peeling, and wiping, which is a common issue with single filler conductive composites composed of LM or AgNWs. The AgNW-LM-elastomer based hybrid composite also facilitated direct laser patterning, which is difficult with LM-based composites. To demonstrate the application of the hybrid composite for stretchable electronics, a laser patterned stretchable heater on textile and a stretchable circuit including a light-emitting diode are fabricated.

Presenting Author: Darpan Shukla North Carolina State University

Presenting Author Biography: Darpan Shukla is a PhD student in the Mechanical and Aerospace Engineering department at NC State University.
She received her B.S. in Mechanical Engineering, and M.S. in Mineral Engineering in 2011 and 2015, respectively. She worked for two years at Tata Steel Limited before joining NC State for her doctorate degree. Her research interests include printed stretchable and flexible electronics.

Authors:

Darpan Shukla North Carolina State University
Hongyu Wang North Carolina State University
Omar Awartani North Carolina State University
Michael D. Dickey North Carolina State University
Yong Zhu North Carolina State University